FIG. 1 shows a typical compressor 20 of a gas turbine engine. The compressor 20 comprises a casing 22 and a plurality of sets of rotor blades 24 mounted for rotation about a longitudinal axis of the compressor 20. Upstream of each set of rotor blades 24 is mounted a set of variable stator vanes 26, each having a first end 28 and a second end 30 rotatably mounted in the casing 22. The first end 28 includes a stator vane spindle 32 mounted for rotation in a bush 34 in the casing 22.
A stator vane actuator ring 36 extends circumferentially around the outside of the casing 22 adjacent to each set of stator vanes 26. Each stator vane spindle 32 is mechanically connected to an adjacent actuator ring 36 by a variable stator vane actuating lever 38. Each actuating lever 38 has a first end 40 pivotally connected to an adjacent actuator ring 36 and a second end 42 immovably attached to an upper end 44 of each vane spindle 32 by a bolt 46 or stud and nut.
Each actuator ring 36 is circumferentially rotatable in either direction about the longitudinal axis of the compressor 20, as indicated by arrow A. This is conventionally achieved by use of an actuating system (not shown). The actuating system may be hydraulic, pneumatic or electric, etc. When an actuator ring 36 is caused to rotate, its rotational movement is transmitted by each of the plurality of actuating levers 38 to the respective stator vane spindles 32 of a set of variable stator vanes 26 causing the spindles 32 to rotate in their respective bushes 34. Rotation of the spindles 32 in turn causes simultaneous rotation of the corresponding set of variable stator vanes 26.
Variable stator vanes are used in gas turbine engines to control airflow through a multi-stage compressor. In the event of breakdown of airflow through the compressor, a condition known as ‘surge’ can occur in which high pressure air is expelled from the combustor into the compressor stages, thereby causing a sudden reversal of the airflow through the compressor and a resultant sudden loss of engine thrust.
Under surge conditions, the reversed airflow can impart a significant shock load onto the variable stator vanes, inducing rotational vibration. Existing variable stator vane actuating levers transmit most of this load to the actuating system, which may cause damage. It would be desirable to reduce the likelihood of such damage occurring in such situations and/or similar situations.